1. Field of the Invention
The invention relates generally to seismic energy vibrators and, more particularly, but not by way of limitation, it relates to an air cushion seismic vibrator and air modulation valve enabling precise control of frequency and wave shape of compressional wave energy input to the earth.
2. Description of the Prior Art
The prior art includes relatively few teachings which relate to seismic energy generation through pressure modulation of an air cushion for coupling seismic wave energy into the earth's surface. A more recent teaching which is directed to an air cushion seismic vibrator attempting particular modulation control is U.S. Pat. No. 3,701,968 in the name of Broding, as issued on Oct. 31, 1972 under title "Air Cushion Seismic Vibrator". This patent reviews the basic concepts and particular modulation approaches in developing an air cushion of sufficient magnitude while maintaining attendant modulation capability. Yet another U.S. Pat. No. 3,792,751 in the name of Fair, as issued Feb. 19, 1974 and entitled "Air Cushion Seismic Signal Source", provides still additional teachings in the development of a sufficiently reliable and strong air cushion seismic source; and this patent is directed to a specific type of air pressure modulator for controlling the entry and exhaust of air to the coupling air cushion at a selected rate.